with multiple documents open in my PC, how do I move seamlessly between (i.e. move back and forth...

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The tutorial fails to explain "Your entire screen" (called something else in my version!); "application Window" or "Chrome tab". I had hoped to open up multiple apps and move between them.I open say tabs (work, powerpoint, excel) in my PC. I need to close the presentation and then re=-share (and often, one of the tabs which I opened , fails to show in the dialogue box. The presentation is disjointed. Any help available please?